Aerobic acetone-butanol-isopropanol (ABI) fermentation through a co-culture of G117 and recombinant 1A1.

An engineered 1A1 strain (BsADH2) expressing a secondary alcohol dehydrogenase (CpSADH) was co-cultured with G117 under an aerobic condition. During the fermentation on glucose, BsADH2 depleted oxygen in culture media completely and created an anaerobic environment for G117, an obligate anaerobe, to grow. Meanwhile, lactate produced by BsADH2 was re-assimilated by G117. In return, acetone produced by G117 was reduced into isopropanol by BsADH2 via expressing the CpSADH, which helped maintain the redox balance of the engineered . In the symbiotic system consisting of two strains, 1.7 ​g/L of acetone, 4.8 ​g/L of butanol, and 0.9 ​g/L of isopropanol (with an isopropanol/acetone ratio of 0.53) was produced from 60 ​g/L of glucose. This symbiotic system also worked when oxygen was supplied to the culture, although less isopropanol was produced (0.9 ​g/L of acetone, 4.9 ​g/L of butanol, and 0.2 ​g/L of isopropanol). The isopropanol titer was increased substantially to 2.5 ​g/L when we increased the inoculum size of BsADH2 and optimized other process parameters. With the - co-culture, switching from the original acetone-butanol (AB) fermentation to an aerobic acetone-butanol-isopropanol (ABI) fermentation can be easily achieved without genetic engineering of . This strategy of employing a recombinant to co-culture with should be potentially useful to modify traditional acetone-butanol-ethanol fermentation for the production of other value-added chemicals.